Light-controlled signaling system



Sept. 27, 1938. F. MICHELSSEN I 2,131,328

LIGHT CONTROLLED SIGNALING SYSTEM Filed April 15, 1935 772922 s??? [as ion F acaor' 3nventor:

F 77? zfc/z elss em Patented Sept. 27, 1938 LIGHT-CONTROLLED SIGNALING svs'rEM F ritz Michel ssen, Berlin-Steglitz, Germany, as-

signor to Neufcldt & Kuhne G. m. b. 11., Kiel,

Germany Application April 15, 1935, Serial No. 16,515

, In Germany Apri1 14, 1934 x 8 Claims (01. 250-51) (Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G. 5)

This invention relates to light-controlled optical systems, more particularly signaling systems and sound-film installations. It is known in optical-signaling systems to modulate the ray of light, coming from a source of light and concentrated by suitable mirrors or lenses, by means of an electrically moved shutter, Kerr-cell or like device in sucha manner that when'the ray of light impinges on a photo-electric cell voltage variations are produced in the rhythm of the light modulation. Such arrangements may be used for telegraphic purposes, as well as for telephony; in the latter case the shutter is electrically operated by the alternating currents in an output circuit of an amplifier, the'input cir-' cult of which contains a' microphone. The devices above referred to have the advantage as compared with other signaling systems, for instance as compared with wireless telegraphy and telephony, that the signal carrier,-that is to say, the wave of light, can'be directed on the receiving apparatus in a very narrow beam so thatthe danger of unauthorized persons hearing or disturbing the transmission is avoided.

In the known systems of light telephony, use is generally made of a source of light which transmits mainly red and infra-red'rays. These rays of light of long wavelength'have theadvantage that they are less absorbed or destroyed by fog or other impurities in the air so that the range of such rays, as compared with'the range of white light, is considerably'increased.

A wave-range of about 0.4 to about 2.5; is now generally available for the transmission of this kind of light telephony. With such a frequency band covering about three octaves, optical apparatus working on a principle of light refraction, more particularly lens systems, have very different properties, For instance, if the incoming ray of light is optically -concentrated at the receiving end on a small point of the receiving cell, it is not possible to unite uniformly all the spectrum ranges transmitted by the original source of light on a. small point orsurface; on the contrary, the optical system will have the optimum effect only for a definite wavelength or a definite narrow wave band, whilst the other waves can be more or less dispersed and are inefl'ective. This is especially detrimental, for instance in the case of light-sensitive cells working on the contact principle. If use is made for the receiving device of a lead sulphide or similarly acting cell in which the received ray is directed, for instance on the contact point of a metal point with a crystal of lead sulphide only a small portion of the incoming energy can be usefully utilized to control the cells, namely thosewaves which are concentrated by'the optical system exactly on to the contact point. The other waves are substantially ineffective. I 5

In the arrangements of light telephony and telegraphy' as hitherto employed, ithas been usual to efiect the optical concentration of the beam of light transmitting the signal purely visually, that is to say, the optical system was adjusted to that part of 'the beam of waves which is visible to the eye; that'is to say, approximately 0.7 to 0.75,u.. .1

Experiments which have been carried outwith respect to sensitiveness'in connection with lead'lfi sulphide cells and other contact and photo-electric cells have shownthat more particularly the lead sulphide cells'have a very great sensitiveness for waves having a length greater than 1.2 and more particularly beyond 1.5a. These ranges of high sensitiveness extend up to more than 2.4

According to the invention, the arrangement is adjusted to the'above last-mentioned wavelengths which actually reach the receiving cell; in contradistinction to the method hitherto employed,- the arrangement is no longer adjusted to the visible part of the transmitted ray of light, but it is dimensioned for the above-mentioned wavelength of more than about 1.2 and more particularly 1.5 With these wavelengths the sensitiveness and, consequently, the efliciency of the whole of the arrangement is considerably increased as compared with arrangements adjusted to the visual wavelength.

The invention may be carried out into effect in various ways. A very useful method is to employ systems of lenses, more particularly on the receiving side,,but also at the transmitter, which lens systems are corrected spherically and chromatically in such a way that-the concentration of the beam of light on the photo-electric cell transmission is most suitable.

According to another arrangement, use is made of filters at the transmitting or receiving end for the filtration of those waves or ranges of 55 waves which lie outside the maximum range of sensitiveness of the receiving cell.

Finally, the source of light is preferably so constructed that it mainly or exclusively transmits infra-red light of those wavelengths -to which the receiving .c'ell shows agmaximuni-. r'e;g-i sponse. In such a case one can operate the apparatus practically without any loss.

The drawing represents byway of example-- the function of the inventionrFig. l-sl'iows' the function of an optical system known in i. .the

5 3 I n a light si'gnaIing system the combination art, Fig. 2 shows the function of the new optical system according to the invention. I In the diagram of Fig. l'andFig scissae represent the wave-length, e p

Ii, the ordinates represent the sensitiveness Of}.

the light-sensitive cell (full lines) and the trans mission factor of the medium 'a'tmospl 'ere (dotted lines).

According to Fig. 1 the maximum sensitiveness; of the cell coincides with the minimum of trans-. mission factor, which gives a very bad eificiency of the entire system. According to Fig. 2 the full line curve represents the sensitiveness of-a lead sulphide .cell, and both curves have nearly the same fonnbetweenOfi and 2.5;i;.that ;givesra very good efficiency, which is further improved by: correcting the employed lenssystem spherically and chromatically in;the waydescribedinthe specification.

Figure 3 illustrates diagrammatically a general arrangement for the transmission ofc-infra-red" light signals. Light, the wave lengths of which lie within the rangeof about 1:2 to about 2 -.5,u.: and more is transmitted iroman infra-red lamp I, the rays of lightgpassing first of all through. an achromatic system of lenses}, and then being concentrated on a point in a shutter. .3. There follows a system of lenses 4,1 preferably' also achromatic, which transmits-therays of lightin the form of a narrow andparal'lel beam." At the receivingend there'is provided achromatic and spherically corrected hollow mirror which :consists in a known manner of a glassportion 5 and a reflecting back surface 6. :This mirror projects the incoming rays of light on alead sulphide. cell 1, workingonthe contact :principle. The. cell comprises a lead sulphidecrystal .8 and a: needle-shaped counter-electrode 9- which rests thereon. The crystal and the needle electrode- 9 are connected to respective leads. The mirror.-

5, 6 concentrates the incoming-rays within the:

range of infra-red waves of about 1.2 to..2.5,i: exactly on to the point contact of the cell 11".:A light filter 9 of suitable substance to transmit only the range of waves desired may 'be associ' ated with the light source as shown- WhatIclaim is: 33 z: m1

1. A light-controlled device comprising incom-- bination a source of lighttransmitting rays, the wave lengths of which lie between about 1.5; and about 2.5 and a lead sulphide cell for receiving the said Waves.

2. Ailight controlleddevice comprising in comi ati rii ai butwiie use ....a i. m ttin l.rays, t wave lengths of which lie between about 1.5;

and about 2.5;i, a lead sulphide contact cell and optical means for focusing the light waves of 1.5 "to 2'. 5,.= '"esact1v tn the contact point of the lead. sulph de. contact .cell.

of a device transmitting rays comprising a wavev bandthe maximal amplitudes of which lie beti a-boutflfiii and about 2.5;i, and a lead sulplii e cell for receiving said waves.

.4..-;In a light-signaling system the combination of a device transmitting rays comprising a wavef bmacnmafimm amplitudes of which lie be- Y "tween bOUtL5/L and about 2.5;, and a lead sulphide. contact cell .i or receiving said waves.

5. Ina light-signaling system the combination-of a .devicetransmitting rays comprising a waveeband ithe. maximal amplitudes of which lie between about 1.5 and about 2.5 a lead sulphidegcell for .receiving said waves, and optical means. which-.are corrected. chromatically to a band of about 1.5 and about 2.5 for focusing the said rays on the cell.

6. In alight-signaling system the combinationtof a device transmitting rays comprising a waveeband the maximal amplitudes of which lie betweenabout 1.5; and about 2.5 a lead sulphide contactcell: foiqreceiving said waves, and optical. means associated with said lead sulphidecontactc ell, which are corrected to a band of. about. l. 5 .o-fQI. concentrating the rays exactly on the; contact. point of said lead sulphide contactcelL- 1 '7. In .a light-signaling system the combination of a device for transmitting rays comprising a Wave-band the maximal amplitudes of which liebetween about 1.5; andabout- 2.5 and a lead sulphide cell ionreceiving said waves, and means comprising; an optical filter adjacent said ray transmitting device for the filtration of those waves rangesqwhicn lie 3 outside the. maximum range of v sensitiveness of .the receiving cell.

-8.:I n.--alight signaling system the combination of a device transmitting'light rayscomprisinga wave-band. .themaximal amplitudes of which lie between about 1.5,". and. about 2.5;i, and .a lead SlllDhldG :cell for receiving said waves, said light transmitting device comprising a sourceof: light soiconstructed that it mainly transmitsnltra-red light of those-.wavelengths towhichsaidreceiving cell shows a maximum response iv I m ivncHELssEN. l 

